Squeeze treatment for in situ scavenging of hydrogen sulfide

ABSTRACT

A method of performing a squeeze treatment comprises pumping a treatment fluid under pressure through a wellbore into a subterranean formation, wherein the treatment fluid includes a hydrogen sulfide scavenging compound that adsorbs onto the subterranean formation in a region around the wellbore. Production fluids are then allowed to flow from the subterranean formation into the wellbore, wherein the production fluids contact the adsorbed hydrogen sulfide scavenging compound as the production fluids flow through the region around the wellbore, and wherein the production fluids contain hydrogen sulfide that reacts with the hydrogen sulfide scavenging compound to reduce an amount of hydrogen sulfide in the production fluids before the production fluids flow into the wellbore.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Nonprovisional patentapplication Ser. No. 14/108,587 filed on Dec. 17, 2013, which claims thebenefit of U.S. Provisional Patent Application No. 61/739,382, filed onDec. 19, 2012.

BACKGROUND

Field of the Invention

The present invention relates to a process of chemical treatment ofproduction fluids in a subterranean formation.

Background of the Related Art

Production fluids that are produced from subterranean formation willoften contain hydrogen sulfide (H₂). Production fluids that include ahigh concentration of hydrogen sulfide are sometimes referred to asbeing “sour” and those production fluids that include little or nohydrogen sulfide are sometimes referred to as being “sweet.” Hydrogensulfide is a toxic and pungent gas and, because it behaves as a weakacid in water, can cause corrosion of steel equipment and pipelines.Natural gas must ordinarily contain less than 4 parts per million (ppm)of hydrogen sulfide before it can be sold. Accordingly, productionfluids may be “sweetened” through a process of removing the hydrogensulfide. Typical hydrogen sulfide removal processes use an activetreatment compound that reacts with the hydrogen sulfide.

Common sweetening processes pass the already produced production fluidsthrough equipment where the hydrogen sulfide is contacted with an activetreatment compound referred to as a “hydrogen sulfide scavenger” or,more simply, a “scavenger.” The hydrogen sulfide scavenger reacts withthe toxic hydrogen sulfide to form a nontoxic compound. Liquidscavengers, for example, may be injected into a pipeline or processingequipment.

BRIEF SUMMARY

One embodiment of the present invention provides a method of performinga squeeze treatment. The method comprises pumping a treatment fluidunder pressure through a wellbore into a subterranean formation, whereinthe treatment fluid includes a hydrogen sulfide scavenging compound thatadsorbs onto the subterranean formation in a region around the wellbore.Production fluids are then allowed to flow from the subterraneanformation into the wellbore, wherein the production fluids contact theadsorbed hydrogen sulfide scavenging compound as the production fluidsflow through the region around the wellbore, and wherein the productionfluids contain hydrogen sulfide that reacts with the hydrogen sulfidescavenging compound to reduce an amount of hydrogen sulfide in theproduction fluids before the production fluids flow into the wellbore.

DETAILED DESCRIPTION

The present invention provides a squeeze treatment including a hydrogensulfide scavenging compound. A “squeeze treatment” is a process ofdelivering a treatment fluid into a treatment zone of a subterraneanformation by pumping the treatment fluid downhole under pressure, thenshutting in the treatment fluid for a period of time to allow thehydrogen sulfide scavenging compound to adsorb onto the surfaces of theformation before producing additional production fluids. In onenon-limiting example, the treatment fluid may be shut in for apredetermined period of time, such as between 12 and 16 hours or perhapslonger. A squeeze treatment may, in accordance with the presentinvention, use a treatment fluid with any of a wide variety of hydrogensulfide scavenging compounds and their combinations.

One embodiment of the present invention provides a method of performinga squeeze treatment for scavenging hydrogen sulfide. The methodcomprises pumping a treatment fluid under pressure through a wellboreinto a subterranean formation, wherein the treatment fluid includes ahydrogen sulfide scavenging compound that adsorbs onto the subterraneanformation in a region around the wellbore. Production fluids are thenallowed to flow from the subterranean formation into the wellbore. Theproduction fluids contact the adsorbed hydrogen sulfide scavengingcompound as the production fluids flow through the region around thewellbore. Accordingly, the hydrogen sulfide in the production fluidswill react with the hydrogen sulfide scavenging compound to reduce anamount of hydrogen sulfide in the production fluids before theproduction fluids flow into the wellbore.

In a further embodiment, the method includes monitoring theconcentration of hydrogen sulfide in the production fluids flowing fromthe subterranean formation through the wellbore. In response to theconcentration of hydrogen sulfide exceeding a threshold concentration,the method may stop the flow of production fluids from the subterraneanformation into the wellbore, then pump an additional amount of thetreatment fluid under pressure through the wellbore into thesubterranean formation, and maintain the treatment fluid in the regionaround the wellbore for a predetermined period of time, beforerestarting the flow of production fluids from the subterranean formationinto the wellbore. In this manner, the amount of the hydrogen sulfidescavenging compound adsorbed onto the surfaces of the subterraneanformation can be replenished at any time that the amount of the hydrogensulfide in the produced fluid begins to rise above a desired level.

Embodiments of the present invention may use any one or more of a broadrange of hydrogen sulfide scavenging compounds. The hydrogen sulfidescavenging compounds may be those having no amine functionalities.However, the hydrogen sulfide scavenging compounds may include moretraditional amine-based hydrogen sulfide scavengers, such as a triazineor amino alcohols such as mono, di or tri-ethanolamine. In a stillfurther embodiment, the hydrogen sulfide scavenging compounds arefunctionalized with a variety of functional groups such as a phosphategroup, phosphonate group, sulfate group, sulfonate group, or hydroxylgroup. In a first option, the hydrogen sulfide scavenging compoundsinclude two phosphate groups or two sulfate groups. In a second option,the hydrogen sulfide scavenging compounds includes at least two hydroxylgroups. The present invention may also use a hydrogen sulfide scavengingcompound that is a reaction product of a carboxylic acid and an aldehyde(alpha-hydroxy alkyl ester) or a reaction product of an alcohol and analdehyde (alpha-hydroxy alkyl ether). These later two classes ofhydrogen sulfide scavenging compounds are described in greater detailbelow.

Embodiments of the invention may use a treatment fluid that includesbetween 5 and 20 volume percent of a hydrogen sulfide scavengingcompound, or between 10 and 15 volume percent of the hydrogen sulfidescavenging compound. Optionally, the treatment fluid may further includea mixture of water and ethanol, such as a 50/50 mixture of water andethanol.

The hydrogen sulfide scavenging compound preferably exhibitsrock-surface adsorption, sulfide/mercaptan scavenging properties, andcompatibility with high brine fluids both before and after the treatmentcompound reacts with sulfide/mercaptan species. After the hydrogensulfide scavenging compound has been introduced into the formation, thecompound absorbs onto the surfaces of the subterranean rock formation.The desired adsorption is provided by the chemical functionalitieswithin the molecular structure of the treatment compound. For example,glycerol bis hemiformal includes three hydroxyl groups and two etherlinkages. It is believed that the oxygenation provided by the hydroxylgroups, ether linkages and other groups such as phosphates and sulfatesprovides the treatment compound with the ability to adsorb onto thesurface of the formation.

After the treatment compound has been successfully squeezed into theformation and adsorbed on the surface of the formation, the pressure inthe well may be reduced to allow formation fluids to be produced fromthe formation and brought up through the well. Typical formation fluidswill include connate water or brine in a mixture with liquid or gaseoushydrocarbons that contain sulfur-containing compounds, such as hydrogensulfide or mercaptans. As those formation fluids flow through theformation toward the well, the adsorbed hydrogen sulfide scavengingcompound will come into contact with the sulfur-containing compounds.The hydrogen sulfide scavenging compound may then react with thesulfur-containing compounds. It should be appreciated that having thetreatment compound adsorbed on the surface of the formation willincrease the contact time with formation fluids, thereby increasing thelikelihood of reacting with more of the sulfur-containing compounds.

Although a squeeze treatment in accordance with the present inventionmay be formulated and performed solely to deliver the hydrogen sulfidescavenging compounds into the formation, a squeeze treatment may alsoinclude other compositions that provide other beneficial effects. Forexample, the squeeze treatment may also include a scale inhibitor.

Due to process limitations in removing hydrogen sulfide from a topsideapplication where the fluids containing hydrogen sulfide have alreadybeen produced from the well, the ratio of hydrogen sulfide scavengingcompound to hydrogen sulfide is typically about 20:1. This ratio islargely a practical function of the small amount of time over which thehydrogen sulfide is in contact with the hydrogen sulfide scavengingcompound. However, when the hydrogen sulfide scavenging compound is partof a squeeze treatment in accordance with the present invention, theproduction fluids pass over the rock that has absorbed the hydrogensulfide scavenging compound. Due to the high amount of surface areawithin this region of the subterranean formation, the contact time ismuch longer and the contact is more efficient. Accordingly, a ratio ofabout 12:1 between the hydrogen sulfide scavenging compound and hydrogensulfide is expected in a squeeze treatment. Furthermore, the squeezetreatment avoids the need for a topside scavenging process, which isparticularly beneficial for a floating production, storage andoffloading (FPSO) or processing facility. Yet another benefit of thepresent squeeze treatment is that the in situ scavenging of hydrogensulfide will continue to scavenge without being affected by topsideprocess outages. By contrast, a simple pump failure can have adevastating affect a topside scavenging process and result in theproduced fluids having a high hydrogen sulfide content.

Alpha-Hydroxy Alkyl Esters

The method may use any one or more of a broad range of alpha-hydroxyalkyl esters as a hydrogen sulfide scavenging compound. One embodimentof the alpha-hydroxy alkyl ester is the reaction product of a carboxylicacid and an aldehyde. Optionally, the carboxylic acid may be a monocarboxylic acid, or an oligomeric or polymeric carboxylic acid.Independently, the carboxylic acid may be saturated, unsaturated oraromatic. The alpha-hydroxy alkyl ester may also contain other productsresulting from the reactions between aldehydes and carboxylic acids, andthey may also be amine-free.

Another embodiment of the alpha-hydroxy alkyl ester has no nitrogen orbasic nitrogen (amine functionalities). In a still further embodiment,the alpha-hydroxy alkyl ester is functionalized with a phosphate group,phosphonate group, sulfate group, sulfonate group, or hydroxyl group. Ina first option, the alpha-hydroxy alkyl ester includes two phosphategroups or two sulfate groups. In a second option, the alpha-hydroxyalkyl ester includes at least two hydroxyl groups.

In a still further embodiment, the hydrogen sulfide scavenger(s) may bereaction product(s) of a monocarboxylic acid, dicarboxylic acid,oligomeric or polymeric carboxylic acid and an aldehyde, dialdehyde,oligomeric aldehyde, or polymeric aldehyde. Accordingly, these reactionproducts may include polyester or cyclic di-esters or some combinationsthereof.

Specific example of alpha-hydroxy alkyl esters that may be used in themethods of the present invention include, without limitation,bis(hydroxymethyl) Maleate; (2E,4E)-hydroxymethyl hexa-2,4-dienoate;(E)-hydroxymethyl but-2-enoate; (E)-bis (hydroxymethyl)O,O′-(2-hydroxypropane-1,3-diyl) difumarate; hydroxymethyl6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoate; sorbic acid, andcombinations thereof.

Generic Structure:

alpha-Hydroxy Alkyl Ester

where: R=aliphatic, cyclic, acyclic, saturated, olefinic, aromatic; andR′═H, aliphatic, cyclic, acyclic, saturated, olefinic, aromatic.

Example Preparation

Specific Examples

bis(hydroxymethyl) maleate

(2E, 4E)-hydroxymethyl hexa-2,2-dienoate

(E)-hydroxymethyl but-2-enoate

(E)-bis(hydroxymethyl) O,O′-(2-hydroxypropane-1,3-diyl) difumarate

hydroxymethyl 6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoate

polyesters Based on Dicarboxylic Acids and Aldehydes

Cyclic Di-Esters Based on Dicarboxylic Acids and Aldehydes

where: R=aliphatic, cyclic, acyclic, saturated, olefinic, aromatic;R₁═H, aliphatic, cyclic, acyclic, saturated, olefinic, aromatic;A=—OH, —OPO₃M, —SO₃M; —PO₃M₂; —OSO₃M

M=H or metal ion; and

n=between 2 and 100 (preferably between 5 and 50, and more preferablybetween 10 and 20).

Alpha-Hydroxy Alkyl Ethers

The method may use any one or more of a broad range of alpha-hydroxyalkyl ethers as a hydrogen sulfide scavenging compound. One embodimentof the alpha-hydroxy alkyl ether is the reaction product on an alcoholand an aldehyde. Another embodiment of the alpha-hydroxy alkyl ether hasno nitrogen or basic nitrogen (amine functionalities). In a stillfurther embodiment, the alpha-hydroxy alkyl ether is functionalized witha phosphate group, phosphonate group, sulfate group, sulfonate group, orhydroxyl group. In a first option, the alpha-hydroxy alkyl etherincludes two phosphate groups or two sulfate groups. In a second option,the alpha-hydroxy alkyl ether includes at least two hydroxyl groups.

In specific embodiments, the alpha-hydroxy alkyl ether is glycerol bishemiformal, glycerol bis hemiformal mono phosphate ether, oligomericglycerol bis hemiformal di-phosphate ether, glycerol bis hemiformal monosulfate ether, oligomeric glycerol bis hemiformal di-sulfate ether, andcombinations thereof. In one example, glycerol bis hemiformal may beformed by the reaction of formaldehyde and glycerol.

Generic Structure:

Alpha-Hydroxy Alkyl Ether

where: R=aliphatic, cyclic, acyclic, saturated, olefinic, aromatic;R′═H, aliphatic, cyclic, acyclic, saturated, olefinic, aromatic; andA=—OH, —OPO₃M, —SO₃M, —PO₃M₂, —OSO₃M.

Example Preparation

A-R—OH+A-R′—(C═O)—H

A-R—O—C(H)(A-R′)—OH

Specific Examples

Glycerol Bis Hemiformal Mono Phosphate Ether

Oligomeric Glycerol Bis Hemiformal Di-Phosphate Ether

Glycerol Bis Hemiformal Mono Sulfate Ether

Oligomeric Glycerol Bis Hemiformal Di-Sulfate Ether

where: M=H or metal ion.

EXAMPLES

Performance Evaluation of Hydrogen Sulfide Scavenging Compounds

The performance of various hydrogen sulfide scavenging compounds wasmeasured using a dynamic testing apparatus. A cadmium chloride solutionwas prepared by adding 125 grams of CdCl₂×2.5H₂O to a small amount ofwater and dilution to 1 liter. Next, a 0.01 molar concentration solutionof HCl is made using 8.5 milliters of concentrated HCl diluted to 1liter. A 0.1N iodine solution and 0.1N Na₂S₂O₃ solution were purchasedfor the iodiometric titrations along with a starch reagent.

A dynamic testing apparatus was used to perform a dynamic test asdescribed in ASTM-D5705. Two sparging flasks were filled with the CdCl₂solution and 15 ml of the 0.01 M HCl solution. The two flasks wereconnected using ⅝″ ID tubing. One of the hydrogen sulfide scavengingcompounds was then placed into an empty sparging flask, which was itselfconnected by tubing to the flasks containing the CdCl₂ solutions. Thesystem was then purged with nitrogen gas to displace any hydrogensulfide from the fluid medium. CdS production is indicated by theformation of a yellow precipitate. A sour fluid sample is dosed with thescavenger chemistry that is to be screened, sealed and placed into aheated mixing oven to simulate heated agitation.

The scrubbed CdS from the flasks is removed once the hydrogen sulfidehas been completely purged and is placed into a beaker for titration. Amagnetic stir bead is added to the beaker and placed onto a stir plate.Iodine solution and starch are added until the mixture has changed tothe color of the iodine. Na₂S₂O₃ was then used to titrate the iodine/CdSmixture. The CdS mixture was then titrated until the solution turnedclear (endpoint). A calculation determined the remaining hydrogensulfide using the results from the titration. This procedure allowed formeasurement of H₂ in the original fluid medium without interference fromthe reaction product of the hydrogen sulfide scavenging compound andH₂S.

TABLE 1 Results of Performance Testing Hydrogen Sulfide Extent ofRemoved in Liquid Reaction Scavenger Composition Phase (%) (%) Glycerolbis-hemiformal 100 19.50 Glycerol hemiformal phosphate ester  94 20.38Triazine 100 25   Glycerol Bis maleic acid adduct  87 25.30 Glycerolpropionic acid adduct  85 29.71 Glycerol Oligomer Bis propionic  8124.43 acid adduct Glycerol oligomer Bis  85 18.28 propionaldehyde adduct

Table 1 shows the efficacy of a hydrogen sulfide scavenging compound interms of the percent of H₂S removed and the percent extent of reaction.The percent of H₂S removed is related to the overall scavenging capacityof the chemical. A high percent of percent of H₂S removed is desired.The percent extent of reaction is calculated based on the ratio of thechemical's theoretical capacity versus the actual capacity. It isdesired to have a high percent extent of reaction indicating that thescavenger molecule is reacting preferentially with the sulfur species toa greater extent so as not to be wasted in the scavenging process.Depending upon the chemical application a more prolonged effect of H₂Smay be desired versus a fast acting scavenging agent.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,components and/or groups, but do not preclude the presence or additionof one or more other features, integers, steps, operations, elements,components, and/or groups thereof. The terms “preferably,” “preferred,”“prefer,” “optionally,” “may,” and similar terms are used to indicatethat an item, condition or step being referred to is an optional (notrequired) feature of the invention.

The corresponding structures, materials, acts, and equivalents of allmeans or steps plus function elements in the claims below are intendedto include any structure, material, or act for performing the functionin combination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but it is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

1. A method, comprising: pumping a treatment fluid under pressurethrough a wellbore into a subterranean formation, wherein the treatmentfluid includes a hydrogen sulfide scavenging compound that adsorbs ontothe subterranean formation in a region around the wellbore; and flowingproduction fluids from the subterranean formation into the wellbore,wherein the production fluids contact the adsorbed hydrogen sulfidescavenging compound as the production fluids flow through the regionaround the wellbore, and wherein the production fluids contain hydrogensulfide that reacts with the hydrogen sulfide scavenging compound toreduce an amount of hydrogen sulfide in the production fluids before theproduction fluids flow into the wellbore.
 2. The method of claim 1,wherein the treatment fluid is maintained in the region around thewellbore for a predetermined period of time to allow the hydrogensulfide scavenging compound to absorb onto the subterranean formation.3. The method of claim 2, wherein the predetermined period of time isbetween 12 and 16 hours.
 4. The method of claim 2, wherein thepredetermined period of time is greater than 16 hours.
 5. The method ofclaim 2, further comprising: monitoring the concentration of hydrogensulfide in the production fluids flowing from the subterranean formationthrough the wellbore; and in response to the concentration of hydrogensulfide exceeding a threshold concentration, stopping the flow ofproduction fluids from the subterranean formation into the wellbore,then pumping an additional amount of the treatment fluid under pressurethrough the wellbore into the subterranean formation, then maintainingthe treatment fluid in the region around the wellbore for apredetermined period of time, and then restarting the flow of productionfluids from the subterranean formation into the wellbore.
 6. The methodof claim 1, wherein the hydrogen hydrogen sulfide scavenging compoundincludes at least one functional group selected from a phosphate group,phosphonate group, sulfonate group and a sulfate group.
 7. The method ofclaim 1, wherein the hydrogen sulfide scavenging compound includes twophosphate groups or two sulfate groups.
 8. The method of claim 1,wherein the hydrogen sulfide scavenging compound includes twophosphonate groups or two sulfonate groups.
 9. The method of claim 1,wherein the hydrogen sulfide scavenging compound includes at least twohydroxyl groups.
 10. The method of claim 1, wherein the hydrogen sulfidescavenging compound is glycerol bis hemiformal.
 11. The method of claim1, wherein the hydrogen sulfide scavenging compound is a reactionproduct of an aldehyde and an alcohol.
 12. The method of claim 1,wherein the hydrogen sulfide scavenging compound is a reaction productof a carboxylic acid and an aldehyde.
 13. The method of claim 12,wherein the hydrogen sulfide scavenging compound is an alpha-hydroxyalkyl ester.
 14. The method of claim 13, wherein the alpha-hydroxy alkylester is functionalized with a phosphate group, phosphonate group,sulfate group, sulfonate group, or hydroxyl group.
 15. The method ofclaim 1, wherein the hydrogen sulfide scavenging compound is a reactionproduct of an alcohol and an aldehyde.
 16. The method of claim 15,wherein the hydrogen sulfide scavenging compound is an alpha-hydroxyalkyl ether.
 17. The method of claim 16, wherein the alpha-hydroxy alkylether is functionalized with a phosphate group, phosphonate group,sulfate group, sulfonate group, or hydroxyl group.
 18. The method ofclaim 1, wherein the hydrogen sulfide scavenging compound is amine-free.19. The method of claim 1, wherein the hydrogen sulfide scavengingcompound is a triazine.
 20. The method of claim 1, wherein the treatmentfluid includes between 5 and 20 volume percent of the hydrogen sulfidescavenging compound. 21.-23. (canceled)